Populating the list from elements of another list

There is a list, named numbers, which is populated twice (returned from some method). I need to store it in another list named total
This is the code i am running

The above code is present in a method which executes twice.

First time the number is returned as 1,6, which is placed in index 0,1 of total. But next time, when again 2 numbers is returned(say, 1, 9),(and i need it to be placed in index 2,3) and my for loop runs, it gives the following
exception : java.lang.IndexOutOfBoundsException: Index: 2, Size: 0

1. Never use get(i) to iterate a List. Use a foreach loop or an explicit Iterator. That way the iteration code will work with any Collection, and should perform consistently for any Collection (or at least perform as well as an iteration can for that particular Collection).

2. The Collection interface specifies an addAll() method, so you can just call list2.addAll(list1);

3. As far as I know, all the Collections in the core API have a constructor that takes another Collection as an argument, so you could do, for instance, list2 = new ArrayList(list1);

As a general rule, when you're looking to do something like this, you should assume you're not the first one to do it, and you should look at the javadocs to see if there's already a facility for doing it.